1. Field of the Invention
The present invention relates to a composition and process for producing foamed glass molded products, and more particularly to a process wherein a mixture of
(a) finely ground glass containing more than 16 weight % alkali metal oxide (hereinafter, glass type A) and
(b) finely ground glass containing less than 16 weight % alkali metal oxide (hereinafter, glass type B) are mixed with water and with foaming agent additives, and optionally fillers, and the mixture is foamed at an elevated temperature.
2. Discussion of the Art
A process for producing foamed glass molded products is disclosed in European Publication No. 0 052 693, which corresponds to U.S. Pat. No. 4,430,107, to present coinventors Dennert and Dennert, the disclosure of which is herein incorporated by reference. In this earlier process, ground glass of glass types A and B, in which 95 weight % have a grain size below 0.1 mm, are used in a weight ratio of A to B ranging from 1:1.5 to 1:20. Suitable glasses containing more than 16 weight % alkali metal oxide are specialty glasses, such as piece glass. Any waste glass, e.g. bottle glass or window glass, can be used as the glass containing less than 16 weight % alkali metal oxide. A mixture of the glasses is prepared which includes water, and preferably water having a temperature ranging from 50 to 95.degree. C., most preferably 95.degree. C. The weight ratio of water to total solids ranges from 1:1.4 to 1:2.5. The blend produced by mixing water and the total solids is briefly stirred in a stirring vessel. Such mixing frequently makes the blended mixture considerably more viscous.
Viscosity can be further increased by the addition of fillers, preferably inorganic fillers. Calcium carbonate in the form or marble, chalk or the like is a preferred filler; however, barium carbonate, dolomite or comparable substances can also be used.
A suitable driving or foaming agent is mixed in with the other ingredients, either before or after the other ingredients are blended together. Used in combination as foaming agents are organic substances, such as sugar and molasses, which may be pyrolyzed at temperatures on the order of 600.degree. C., to release carbon and carbon monoxide gas, and substances which release oxygen gas, such as pyrolusite (MnO.sub.2), when heated at temperatures on the order to 700 to 900.degree. C. These driving or foaming agents can be added to the starting materials or to the blended mixture produced therefrom. Depending on the desired shape of the end product, the blended ingredients are either granulated or poured into molds. The term "molded products" as used herein is intended to include molded plates or other cast bodies, as well as, granules. The granules or cast pieces (for example, molded plates) are then foamed at an elevated temperature, for example, at a temperature ranging from 700 to 900.degree. C.
The earlier process of European Publication No. 0 052 693 has been found satisfactory from a technical point of view. The resulting foamed glass molded products have a low weight per unit volume ranging from 0.1 to 1.1 g/cm.sup.3 and good strength. However, foamed glass molded products of the above-described type are typically employed as auxiliary construction materials and must be manufactured as inexpensively as possible. As is known, the price of such products depends in part on the cost of the raw materials employed. In the present case, the cost of the required quantity of specialty glass containing more than 16 weight % alkali metal oxide represents the most costly raw material.